1. Field of the Invention
The instant invention relates to an apparatus for diffusing reflected light, such as that from a reflective TFT-LCD (Thin Film Transistor-Liquid crystal display), into a desired solid angle which can be deviated from the unpleasant high intensity specular ray usually produced by the covering glass.
2. Description of the Related Art
To facilitate later discussion, we first define the optics terms and variables that shall be used, as shown in FIG. 1. An incident plane is the plane containing the incident ray and the normal direction of the reflection point. A specular ray is defined as the reflected light ray on the incident plane whose reflected angle is equal to the incident angle. The light cone subtended by the diffused light is called a diffused light cone. Define the distribution angle of the diffused light cone in the incident plane as the vertical diffusion angle, .theta..sub.S, and that perpendicular to the incident plane as the horizontal diffusion angle, .theta..sub.T. A deviation angle .theta..sub.0 is the angle between the specular ray and the central ray in the diffused light cone.
Traditional reflective light diffusing elements, such as diffusive films (e.g., the Poloroid Holographic Reflector and Sumitomo Lumisty) or bump reflectors (e.g., U.S. Pat. No. 5,610,741 and R.O.C. Patent No. 255,019), can not simultaneously achieve the goals of controlling the size of the diffused light cone, directing the reflected light distribution away from the specular ray, keeping the resolution power, and preventing from color dispersion. However, for certain applications the specular ray reflected by the covering glass is undesired because it is glare of the virtual image of the light source, and also, owing to the user's viewing angle, one side of the usual diffused light cone around the specular ray will be useless. Since the efficiency of usual reflective TFT-LCDs is already as low as 10%, extra waste of diffused light will demand a stronger light source and thus cause further increase in the cost. Therefore, effectively controlling and smoothly distributing diffused light within specific solid angle to yield higher intensity and more thorough use of reflected light from a reflective liquid crystal display (LCD) will be of great practical value.
One way to improve the above situation is by combining a diffusive film with a slant reflector structure. Although a diffused reflective light away from the specular ray can be achieved in this way, yet this method obviously increases the structure cost and, as a drawback of usual diffusive films, decreases the resolution of the LCD and causes the color dispersion problem.